The present invention relates to a process for removing arsenic impurities from anhydrous hydrogen fluoride. More specifically, this invention relates to a process for removing arsenic impurities from anhydrous hydrogen fluoride at a substantially increased rate by treating anhydrous hydrogen fluoride with elemental chlorine in combination with either anhydrous hydrogen chloride or a fluoride salt.
Anhydrous hydrogen fluoride is manufactured by heating a mixture of fluorspar and sulfuric acid. The main impurities in anhydrous hydrogen fluoride produced by this method are water, sulfuric acid, fluorosulfonic acid, silicon tetrafluoride, fluorosilicic acid, hydrogen sulfide, and sulfur dioxide. These impurities are conveniently removed by fractional distillation and the resulting anhydrous hydrogen fluoride typically has a purity of about 99.8% or better. Minor amounts of certain other undesirable impurities such as arsenic, phosphorus, and sulfur are usually present in anhydrous hydrogen fluoride produced by this method. The amounts of the impurities such as arsenic which are present in the anhydrous hydrogen fluoride depend on the amounts of these impurities in the fluorspar from which the anhydrous hydrogen fluoride is produced. The presence of these minor impurities, especially arsenic, in the anhydrous hydrogen fluoride is highly undesirable in many applications. Anhydrous hydrogen fluoride is used in the refining and chemical manufacturing industries and arsenic impurities in the hydrogen fluoride can poison catalysts and contaminate the manufactured products which adversely affects the product quality. In the electronics industry, aqueous solutions of hydrogen fluoride are used as cleaning agents and etchants in the manufacture of semi-conductors, diodes, and transistors. A high degree of purity and extremely low levels of impurities such as arsenic are required to prevent contamination of the surface of these electronics industry products which adversely affects their performance.